Cement, portland, chemicals

Description

Portland cement refers to a class of hydraulic cements in which the two essential constituents are tricalcium silicate (3CaO·SiO2) and dicalcium silicate (2CaO·SiO2) with varying amounts of alumina, tricalcium aluminate, and iron oxide. It is insoluble in water. The quartz content of most finished cements is below 1%. Chromium may be present.

Chemical Properties

odourless fine white to grey powder

Uses

The majority of the cement used in construction is mixed with sand and gravel and water at a central plant and trucked wet to the construction site. Thus, there is little opportunity for exposure of workers at the site to cement dust. Nevertheless, many construction workers may be exposed to cement dust when small amounts are mixed on site or when cement or concrete materials are cut or ground.

Definition

A type of hydraulic cement in the form of finely divided, gray powder composed of lime, alumina, silica, and iron oxide as tetracalcium alumino- ferrite (4Ca O?Al 2 O 3 ?Fe 2 O 3 ), tricalcium aluminate (3Ca O?Al 2 O 3 ), tricalcium silicate (3Ca O?Si O 2 ), and dicalcium silicate (2Ca O?Si O 2 ). These are abbreviated, respectively, as C 4 AF, C 3 A, C 3 S, and C 2 S. Small amounts of magnesia, sodium, potas- sium, and sulfur are also present. Hardening does not require air and will occur under water. Cement may be modified with various plastic latexes in pro- portions up to 0.2 part latex solids to one part cement to improve adhesion, strength, flexibility, and cur- ing properties. Water evaporation can be retarded by adding such resins as methylcellulose and hydrox- yethylcellulose. For further information, refer to the Portland Cement Association, 5420 Old Orchard Road, Skokie, IL 60077-1083.

General Description

A gray to white, odorless powder. A finely ground (powdered) mixture of mainly 3CaO.SiO2 (tricalcium silicate), 2CaO.SiO2 (dicalcium silicate), CaO.Al2O3 (tricalcium aluminate), 4CaO.Al2O3.Fe2O3(tetracalcium aluminoferrite) and CaSO4.2H2O (calcium sulfate dihydrate).

Reactivity Profile

Sets in an exothermic reaction to a solid of low strength within hours after mixing with water. Continuing slower exothermic reactions harden the product to a tough gray stony mass. Incompatible with acids, acid chlorides, and acid anhydrides when set. Incompatible with ammonium salts and aluminum metal when wet and unset.

Hazard

Pulmonary function effects, asthma, respi- ratory symptoms. See concrete (1).

Health Hazard

Portland cement is an irritant of the eyes and causes dermatitis.

Safety Profile

A nuisance dust. A skin irritant. See also NUISANCE DUSTS and AEROSOLS.

Carcinogenicity

Earlier studies have suggested increases in various types of cancer, including lung and stomach, with exposure to cement, but numerous limitations prevent any conclusions in this regard.

Raw materials

Preparation Products